Assembly of a fluorescent lamp and an extension means

ABSTRACT

An energy-saving assembly of an elongate low-pressure mercury vapor discharge lamp ( 1 ) and at least one elongate extension means ( 2 ). The low-pressure mercury vapor discharge lamp comprises a light-transmitting discharge vessel ( 10 ) enclosing, in a gastight manner, a discharge space ( 15 ) provided with a filling of mercury and a rare gas mixture. The rare gas mixture comprises at least 50% by volume of krypton. The discharge vessel is provided with a luminescent layer ( 13 ). Electrodes ( 4   a;    4   b ) are arranged in the discharge space for maintaining a discharge in the discharge space. The extension means are provided for connection to the low-pressure mercury vapor discharge lamp. The extension means comprises an inductance ( 3 ). The length of the low-pressure mercury vapor discharge lamp together with the length of the extension means is adapted to fit a pre-determined mounting distance of low-pressure mercury vapor discharge lamps.

The invention relates to an assembly of an elongate low-pressure mercuryvapor discharge lamp and at least one elongate extension means.

The invention also relates to a low-pressure mercury vapor dischargelamp for use in the assembly.

The invention also relates to an extension means for use in theassembly.

In mercury vapor discharge lamps, mercury constitutes the primarycomponent for the (efficient) generation of ultraviolet (UV) light. Aluminescent layer comprising a luminescent material (for example, afluorescent powder) may be present on an inner wall of the dischargevessel to convert UV to other wavelengths, for example, to UV-B and UV-Afor tanning purposes (sun panel lamps) or to visible radiation forgeneral illumination purposes. Such discharge lamps are therefore alsoreferred to as fluorescent lamps. The discharge vessel of a low-pressuremercury vapor discharge lamp is usually tubular and circular incross-section.

In recent years much knowledge has been gained about (elongate)low-pressure mercury vapor discharge lamps, for instance TLD lamps, andtheir properties. Low-pressure mercury vapor discharge lamps are wellestablished in the market. In general, two varieties of low-pressuremercury vapor discharge lamps exist. A first group of low-pressuremercury vapor discharge lamps comprises “standard” colors with aluminescent layer comprised of halophosphate material with relativelylow lumens and a relatively low efficacy (lm/W), as well as a relativelylow maintenance and a relatively low color rendering. A second group oflow-pressure mercury vapor discharge lamps comprises so-calledtri-phosphor lamps with a luminescent layer comprised of three or morerare-earth-containing phosphors with a relatively high lumen output, arelatively high efficacy (lm/W), a better maintenance, and an improvedcolor rendering. Users of the first group of low-pressure mercury vapordischarge lamps are often reluctant to switch to the second group oflow-pressure mercury vapor discharge lamps with the tri-phosphortechnology because these discharge lamps represent a substantialinvestment with relatively little cash payback, in that the low-pressuremercury vapor discharge lamps of the second group give more light, butno energy savings in an existing installation. For this reason sales offluorescent lamps with tri-phosphor technology are primarily driven bynew installations. The market for “standard” color low-pressure mercuryvapor discharge lamps is driven primarily by cost and these productshave become commodities with vanishing margins.

An assembly of an elongate low-pressure mercury vapor discharge lamp andat least one elongate extension means is known from U.S. Pat. No.4,163,176. In the known assembly, a fluorescent lamp having an extensionbase at one end thereof containing an impedance is provided for reducinga current flow through the discharge lamp. The length of the dischargelamp plus extension base equals the length of “standard” fluorescentlow-pressure mercury vapor discharge lamps.

It is an object of the invention to provide an assembly of an elongatelow-pressure mercury vapor discharge lamp and at least one elongateextension means which consumes less energy. According to the invention,an assembly of an elongate low-pressure mercury vapor discharge lamp andat least one elongate extension means is provided:

the low-pressure mercury vapor discharge lamp comprising:

-   -   a light-transmitting discharge vessel enclosing, in a gastight        manner, a discharge space provided with a filling of mercury and        a rare gas mixture,    -   the rare gas mixture comprising at least 50% by volume of        krypton,    -   the discharge vessel being provided with a luminescent layer,    -   electrodes being arranged in the discharge space for maintaining        a discharge in the discharge space,

the elongate extension means being provided for connection to thelow-pressure mercury vapor discharge lamp,

the extension means comprising an inductance,

the length of the low-pressure mercury vapor discharge lamp togetherwith the length of the extension means being adapted to fit apre-determined mounting distance of low-pressure mercury vapor dischargelamps.

The inventors have recognized how to reduce the wattage of thelow-pressure mercury vapor discharge lamp by reducing the lamp lengthwhile maintaining the retrofittability in a “standard” low-pressuremercury vapor discharge lamp system with a pre-determined mountingdistance. According to the invention, a low-pressure mercury vapordischarge lamp with a reduced length of the discharge vessel and with arelatively high krypton content in the rare gas mixture is provided incombination with an extension means comprising an inductance. In orderto maintain retrofittability in “standard” low-pressure mercury vapordischarge lamp systems, an elongate extension means is fitted to one orto both ends of the low-pressure mercury vapor discharge lamp in theassembly according to the invention such that the assembly of thelow-pressure mercury vapor discharge lamp and the extension means fitsin existing fixtures and complies with discharge lamp length standards.

An advantage of providing an elongate extension means is that additionalelectronic components can be incorporated in the extension means. Suchelectronic components further adjust electrical parameters of thelow-pressure mercury vapor discharge lamp system in a favorable manner.The inductance provided in the extension means acts to reduce thecurrent in the entire assembly resulting in power savings both in thelow-pressure mercury vapor discharge lamp and in the external ballastcircuit.

The assembly according to the invention allows users to upgrade theirdischarge lamp systems with lower wattage while yielding substantiallythe same lumens and a substantial saving in operating costs. Additionalbenefits include improved lumen maintenance (higher average lumens),longer life, and lower mercury content, as well as reduced waste upondisposal. The assembly according to the invention has the additionaladvantage that, due to the lower voltage of the discharge lamp and ashorter discharge length, it improves some of the issues hampering usersin countries with unstable line voltage, such as better ignition andlower extinction voltage.

Preferably, the rare gas mixture in the discharge vessel of thelow-pressure mercury vapor discharge lamp comprises at least 80% byvolume of krypton. Additional wattage reduction is achieved byincreasing the amount of krypton in the rare gas mixture. In analternative embodiment, xenon is employed instead of krypton.

A preferred embodiment of the assembly according to the invention ischaracterized in that the gas pressure in the discharge vessel of thelow-pressure mercury vapor discharge lamp is between 10⁵ and 4·10⁵ Pa(between 1 and 4 mbar), preferably between 2·10⁵ and 3·10⁵ Pa (between 2and 3 mbar). Although a filling pressure higher than 3·10⁵ Pa willresult in an additional wattage reduction and a slightly lower efficacyit will cause difficult ignition on many ballast systems. Pressureslower than 2·10⁵ Pa could enhance starting and efficacy, but wattage andlumens would be higher, so a higher krypton content and/or inductance inthe extension means would be necessary to reduce the wattage. Lifetimewill also be reduced with lower filling pressure. Generally speaking,requirements with respect to rare gas mix, filling pressure andinductance are interrelated. The desired wattage reduction can beachieved in a number of ways, with consequences for lifetime, lumens,efficacy, and ignition. A particularly preferred range is from 2·10⁵ to2.4·10⁵ Pa.

Experiments have shown that the inductance can be chosen such that thepower savings in the external ballast circuit are greater than or equalto the power losses in the extension means. To this end, a preferredembodiment of the assembly according to the invention is characterizedin that the impedance of the inductance in the extension means is in arange of between 5% and 30% of the inductance of an external ballastcircuit for the low-pressure mercury vapor discharge lamp. A relativeimpedance of the inductance in the extension means greater than 30% istoo large and would reduce by too great a factor the light output of thelow-pressure mercury vapor discharge lamp. The absolute value of theimpedance of the inductance in the extension means for a TL40/FLD36inductive ballast system (390 Ohms) is in the range from 20 to 120 Ohmsat a frequency of 50 Hz. A preferred value of the relative impedance ofthe inductance in the extension means is 15%, corresponding to a valueof approximately 60 Ohms at 50 Hz. Other values apply for lamps systemsof different wattage, e.g. 18 W and 58 W.

In a preferred embodiment of the assembly according to the invention,the ratio of the length l_(em) of the extension means to the lengthl_(dl) of the low-pressure mercury vapor discharge lamp is in a rangeof: $0.8 \leq \frac{l_{dl}}{l_{{dl} + l_{em}}} \leq {0.98.}$If the length of the low-pressure mercury vapor discharge lamp isreduced by more than 20%, a substantial “dark” area will be present inthe fixture. In addition, the light distribution will be adverselyaffected. In keeping with these requirements it is desirable not toreduce lamp length by more than 10%. Preferably, the length of thelow-pressure mercury vapor discharge lamp is in a range from 0.92 and0.97.

The extension means may form an integral part of the low-pressuremercury vapor discharge lamp or may be supplied separately for re-use.In an alternative, preferred embodiment of the assembly according to theinvention, the extension means comprises two elongate extension parts,the length of the low-pressure mercury vapor discharge lamp togetherwith the lengths of the two extension parts being such as to fit thepredetermined mounting distance of low-pressure mercury vapor dischargelamps. In a further alternative, preferred embodiment of the assemblyaccording to the invention, the extension means forms an integral partof the low-pressure mercury vapor discharge lamp.

According to the invention as described above, the extension means isused to reduce the current in the low-pressure mercury vapor dischargelamp in order to achieve the desired wattage reduction. The space forthe extension means is made available by the reduced length of thelow-pressure mercury vapor discharge lamp itself.

An additional problem of the assembly of the low-pressure mercury vapordischarge lamp and the extension means containing the inductance is thatthe inductance will be in series with one pin issuing from a lamp cap ofthe low-pressure mercury vapor discharge lamp when the extension meansis assembled with the low-pressure mercury vapor discharge lamp. Whenthe assembly of the low-pressure mercury vapor discharge lamp and theextension means is placed in an existing luminaire, it may be insertedin four different orientations. With respect to the external ballastcircuit, the inductance will alternately be installed in the externalballast circuit (“desired” installation) or in the external startercircuit (“misapplication”). It is an additional object of the inventionto provide a solution whereby the customer is notified if theinstallation is wrong and/or the situation is self-correcting.

To this end, a preferred embodiment of the assembly according to theinvention is characterized in that the extension means is provided withan indicator means for indicating the status of the connection betweenthe extension means and an external ballast circuit and an externalstarter circuit for the low-pressure mercury vapor discharge lamp.

A favorable way to provide the indicator means is that the indicatormeans comprises a light emitting diode (LED) connected across turns ofthe inductance. The indicator means may either be a positive indicator(desired installation) or a negative indicator (misapplication). Anexample of a “positive” indicator means is a (green) LED connectedacross (several turns of) the inductance in the extension means. Thevoltage generated across the (turns of the) inductance during properlamp operation causes the LED to glow green. If the extension means isinstalled “wrongly”, such that the inductance is in the external startercircuit, no current will flow in the inductance during lamp operationand the LED will not light up.

An alternative, favorable way to provide the indicator means is that theextension means comprises a resistor and the indicator means comprises alight emitting diode (LED) connected across the resistor. If theresistor is in the external starter circuit (desired installation),current will flow only during starting of the low-pressure mercury vapordischarge lamp. With a “wrong” installation (inductance in the externalstarter circuit and resistor together with LED in the external ballastcircuit), current will flow through the resistor, thus generating avoltage which will light the LED.

An embodiment of the assembly according to the invention ischaracterized in that the indicator means comprises a thermal indicator.Such thermal indicators are also used in some batteries to indicatetheir charging state. The thermal indicator may either be a “positive”indicator triggered by the heat generated by the inductance or a“negative” indicator triggered by the heat generated by a resistanceplaced in the non-inductive circuit of the extension means. Thisembodiment of the invention is robust and inexpensive but may have arelatively slow response time (the discharge lamp has to burn forseveral minutes to get an indication).

A very favorable solution involves an automatic switching adapter. Tothis end the extension means comprises an automatic switching adapterproviding that the inductance is automatically connected to the externalballast circuit independently of the installation orientation after theextension means have been connected to the low-pressure mercury vapordischarge lamp and the assembly has been placed in a “standard” externalballast circuit and a “standard” external starter circuit.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1A is a cross-sectional view of an elongate low-pressuremercury-vapor discharge lamp according to the prior art;

FIG. 1B is a cross-sectional view of an assembly according to theinvention with an elongate low-pressure mercury vapor discharge lamp andwith two elongate extension means;

FIG. 1C is a cross-sectional view of an assembly according to theinvention with an elongate low-pressure mercury vapor discharge lamp andwith one elongate extension means;

FIG. 2 shows an assembly according to the invention with an elongatelow-pressure mercury vapor discharge lamp and an elongate extensionmeans connected to an external starter circuit and an external ballastcircuit;

FIG. 3A shows an elongate extension means provided with an indicatormeans according to the invention;

FIG. 3B shows an elongate extension means provided with an alternativeindicator means according to the invention;

FIG. 4 shows an elongate extension means provided with an automaticswitching adapter according to the invention, and.

FIG. 5A and 5B shows two switching modes of the extension means in FIG.4.

The Figures are purely diagrammatic and not drawn to scale. Notably,some dimensions are shown in a strongly exaggerated form for the sake ofclarity. Similar components in the Figures are denoted as much aspossible by the same reference numerals.

FIG. 1A is a diagrammatic a cross-sectional view of an elongatelow-pressure mercury-vapor discharge lamp 1 according to the prior art.The prior art low-pressure mercury vapor discharge lamp 1 comprises alight-transmitting discharge vessel 10. The discharge vessel 10 enclosesa discharge space 15 in a gastight manner. Electrodes 4 a; 4 b mountedon end portions 14 a; 14 b are arranged in the discharge space 15 formaintaining a discharge in the discharge space 15. The electrodes 4 a; 4b are windings of tungsten covered with an electron-emitting substance,normally a mixture of barium oxide, calcium oxide and strontium oxide.Current-supply conductors extend from the electrodes 4 a; 4 b, passthrough the end portions 14 a; 14 b, and issue to outside the dischargevessel 10. The discharge space 15 is provided with a filling of mercuryand a rare gas mixture. In addition, the discharge vessel 10 is providedwith a luminescent layer 13. The luminescent layer 13 is preferablyprovided on a surface of the discharge vessel 10 facing the dischargespace 15. The luminescent layer 13 includes a luminescent material (forexample a fluorescent powder) which converts the ultraviolet (UV) lightgenerated by fallback of the excited mercury into (generally) visiblelight. The length of the prior art low-pressure mercury vapor dischargelamp 1 in FIG. 1A is fixed to a pre-determined mounting distance l_(md)of low-pressure mercury vapor discharge lamps.

FIG. 1B is a diagrammatic a cross-sectional view of an assemblyaccording to the invention with an elongate low-pressure mercury vapordischarge lamp 1 and with two elongate extension means 2 a, 2 b. Therare gas mixture in the discharge vessel 10 comprises at least 50% byvolume of krypton. Preferably, the gas mixture comprises at least 80% byvolume of krypton. The elongate extension means 2 a; 2 b are providedfor connection to the low-pressure mercury vapor discharge lamp 1. Thelength l_(dl) of the low-pressure mercury vapor discharge lamp 1together with the lengths l_(em) of the two extension means 2 a; 2 b isadapted to fit the pre-determined mounting distance l_(md) oflow-pressure mercury vapor discharge lamps. The length of the extensionmeans with reference numeral 2 a may be different from the length of theextension means with reference numeral 2 b.

FIG. 1C is a schematic a cross-sectional view of an assembly accordingto the invention with an elongate low-pressure mercury vapor dischargelamp 1 and with one elongate extension means 2. The rare gas mixture inthe discharge vessel 10 comprises at least 50% by volume of krypton.Preferably, the gas mixture comprises at least 80% by volume of krypton.The elongate extension means 2 is provided for connection to thelow-pressure mercury vapor discharge lamp 1. The length l_(dl) of thelow-pressure mercury vapor discharge lamp 1 together with the lengthl_(em) of the extension means 2 is adapted to fit the pre-determinedmounting distance l_(md) of low-pressure mercury vapor discharge lamps,in other words l_(dl)+l_(em)=l_(md).

According to the invention, the wattage of the low-pressure mercuryvapor discharge lamp is reduced owing to the lamp length whilemaintaining the retrofittability in a “standard” low-pressure mercuryvapor discharge lamp system with a predetermined mounting distance. Thelow-pressure mercury vapor discharge lamps according to the invention asshown in FIGS. 1B and 1C fits in existing fixtures and complies withlamp length standards. The space for the extension means 2 is providedby the reduced length of the low-pressure mercury vapor discharge lamp1.

Preferably, the ratio of the length l_(em) of the extension means to thelength l_(dl) of the low-pressure mercury vapor discharge lamp is in arange of: ${0.8 \leq \frac{l_{dl}}{l_{dl} + l_{em}} \leq 0.98},$Preferably, the length of the low-pressure mercury vapor discharge lampis in a range from 0.92 to 0.97. In experiments, the length reductionwas approximately 5%, leaving ample space to incorporate the desiredelectronic components (e.g. the inductance) in the extension means.

The elongate low-pressure mercury vapor discharge lamp 1 in FIG. 1A hasa “standard” length of l_(md)=1200 mm if it is of the standard 36 W TLDdesign. By way of example, a favorable length of the energy-savinglow-pressure mercury vapor discharge lamp 1 lamp of FIG. 1B and 1C isl_(dl)=1150 mm (length reduction is approximately 4.2%). Thecorresponding length of the extension means 2 in FIG. 1C is l_(em)=50mm.

The following data are given by way of example. In all cases presentedbelow, the low-pressure mercury vapor discharge lamp referred tocomprises a luminescent layer on the basis of tri-phosphor technology ina mixture to give a color temperature of 6,500K on the black body locus.A length reduction of 50 mm alone gives a low-pressure mercury vapordischarge lamp in an assembly according to the invention with a lampvoltage 97 V, a lamp current of 449 mA, a lamp wattage of 35.6 W, and alamp efficacy of 86.5 lm/W as compared with a TLD36 with a lamp voltageof 103 V, a lamp current of 440 mA, a lamp wattage of 36.5 W, and a lampefficacy of 85 lm/W. If, in addition, the rare gas mixture is adjustedfrom 3·10⁵ Pa/75% Kr to 2.4·10⁵ Pa/90% Kr, this gives a lamp voltage of92 V, a lamp current of 456 mA, a lamp wattage of 34.5 W, and a lampefficacy of 85.6 lm/W for the low-pressure mercury vapor discharge lampin the assembly according to the invention. Addition of a 60Ω impedanceresults in a relatively large reduction in wattage. For a low-pressuremercury vapor discharge lamp with a rare gas mixture of 2.0·10⁵ Pa/75%Kr this results in a lamp voltage of 102.4 V, a lamp current of 377 mA,a lamp wattage of 31.8 W, and a lamp efficacy of 88.2 lm/W. For alow-pressure mercury vapor discharge lamp with a rare gas mixture of2.4·10⁵ Pa/90% Kr this results in a lamp voltage of 96.8 V, a lampcurrent of 384 mA, a lamp wattage of 30.6 W, and a lamp efficacy of 88.5lm/W. The presence of the additional impedance results in an increasedefficacy. In addition, the savings in system current through theexternal ballast circuit result in power savings that offsets any lossesgenerated in the inductance present in the extension means. In theabsence of an additional inductance, the wattage of the discharge lampis reduced only slightly and this will be offset by additional heatinglosses in the external ballast circuit due to increased lamp currentresulting in minimal, if any, system wattage reduction. For alow-pressure mercury vapor discharge lamp with a length reduction of 50mm and a rare gas mixture filling of 2.4·10⁵ Pa/90% Kr and comprising aluminescent layer with tri-phosphor technology and a color temperatureof 6,500K on the black body locus, the lamp efficacy is approximately26% higher than that of the “standard” daylight color low-pressuremercury vapor discharge lamp TLD36/54. In this case, the lamp wattagehas been reduced by 16.2%. The energy-saving low-pressure mercury vapordischarge lamp in this preferred embodiment of the assembly still emitssubstantially more lumens than the “standard” lamp. These extra lumenscan be used for additional wattage savings, as an additional marketadvantage over “standard” color, or as a means for reducing product cost(savings in phosphor materials because lower lumen/efficacy target isneeded to give same luminous as “standard” color). Efficacy comparisonsare given for illustration only and may differ for other chromaticities.

A reduced length of 50 mm gives the low-pressure mercury vapor dischargelamp, in operation, a discharge voltage of approximately 97 V (asagainst 103 V for a “standard” low-pressure mercury vapor dischargelamp) and a wattage of the discharge lamp on TLD36/TL40 ballast circuitsof approximately 35.6 W (as against 36.5 W for a “standard” low-pressuremercury vapor discharge lamp).

The invention has the additional advantage that it eliminates some ofthe issues hampering users in countries with unstable line voltage fromconverting from TL to TLD. The first issue involves the more difficultnature of TLD lamp ignition due to the Kr gas filling. In the lampdesign mentioned above, the reduced discharge length and lower lampvoltage will serve to reduce the starting requirements. The second issueinvolves the extinction voltage of the lamp. Operating TLD lampsnormally extinguish when the line voltage is reduced to belowapproximately 155 V as compared with approximately 140 V for TL. Thereduced lamp voltage of the discharge vessel with reduced length largelyeliminates this performance difference. This implies that the inventionallows many users to upgrade from 40 W to 30 W systems yielding the samelumens and saving 25% of operating costs. Additional benefits includeimproved lumen maintenance (higher average lumens), longer life, andlower mercury content, as well as reduced waste upon disposal.

FIG. 2 shows an elongate low-pressure mercury vapor discharge lamp 1provided with an elongate extension means 2 according to the inventionconnected to an external starter circuit 9 and an external ballastcircuit 8. In the example of FIG. 2, the external starter circuit 9 is aso-called glow-switch starter. The extension means 2, preferably,provides the means for reducing the current through the discharge lampand assists in achieving the desired wattage. To this end, the extensionmeans 2 comprises an inductance 3. Preferably, the impedance of theinductance 3 in the extension means 2 is in a range between 5% and 30%of the inductance of an external ballast circuit 8 for the low-pressuremercury vapor discharge lamp. A favorable combination of the extensionmeans 2 comprising a 60Ω inductive impedance combined with a reductionin lamp length of 60 mm gives approximately 30.5 W in the discharge lampwhen combined with a “standard” external ballast circuit.

The extension means 2 with inductance 3 according to the invention isfeasible both economically and in size (for example fits in a tubularpackage of T8 diameter in the length made available by the lamp lengthreduction). In addition, the extension means 2 may be designed to matewith a special cap at one end of the low-pressure mercury vapordischarge lamp 1 with a reduced length of its discharge vessel 10. Inaddition, the discharge lamp and the extension means 2 may be lockedtogether, integrally forming a single unit that in every respect fulfilsthe dimensional requirements of a “standard” TLD36 low-pressure mercuryvapor discharge lamp. The extension means 2 with inductance 3 has arelatively long lifetime due to the absence of active electricalcomponents inside. This will enable the adapter to be re-used over manylamp lives, thus increasing the payback of such an assembly for thecustomer.

The use of an extension means 2 according to the invention creates anadditional source of system losses due to the heat generated in theturns of the inductance 3. However, the inductance 3 also reduces thecurrent in the entire assembly resulting in power savings in theexternal ballast circuit 8. It was shown in feasibility studies that thedesign can be chosen such that the power savings in the external ballastcircuit 8 are greater than or equal to the power losses in the extensionmeans 2.

A number of embodiments will now be presented in order to enable thecustomer to discern whether the installation of the extension means hasbeen performed correctly.

A “positive” indicator is used in a first embodiment a”. FIG. 3A showsan elongate extension means provided with an indicator means 2 accordingto the invention. In the example of FIG. 3A, the indicator means 18 is a(green) light emitting diode (LED) connected across several turns of theinductance 3 in the extension means 2. The voltage generated acrossthese turns during proper lamp operation will cause the LED to glow(green). If the extension means 2 is installed “wrongly”, such that theinductance is in the external starter circuit 9, no current will flow inthe inductance 3 during lamp operation and the LED will not light. Notethat the LED might flicker during starting in both “right” and “wrong”installations. If the user/installer notes that the LED is not litduring operation, he may either rotate the discharge lamp in the fixtureor—if a switch is provided on the adapter—move the switch to theopposite position.

In a second embodiment, a “negative” indicator is used. FIG. 3B shows anelongate extension means 2 provided with an alternative indicator meansaccording to the invention. In the example of FIG. 3B, the indicatormeans 19 is a (red) LED connected across a resistor 7 inserted in theline parallel to the line in the extension means 2 containing theinductance 3. If the resistor 7 is in the external starter circuit 9(correct installation), current only flows during starting the dischargelamp. While this low ohmic resister will reduce the starting currentslightly, this will have only a minor effect on starting behavior andcan be compensated for in the lamp coil design. With a “right” adapterinstallation, the red LED may flicker during starting, but will be offduring lamp operation. With a “wrong” installation (the inductance 3 inthe external starter circuit 9 and the resistor 7 together with LED inthe external ballast circuit), current will flow through the resistor 7,thus generating a voltage which will light the LED. The LED will lightup only during incorrect installation (resistor 7 does not cause lossesin correct installation). In incorrect installation, the resistor 7 canalso help to limit excessive current being drawn from the externalballast circuit 8 (making up for some/all of the missing lamp voltagefrom reduced lamp length). With this type of indicator means 19, theuser/installer will have to look for red LEDs after installation androtate the respective lamps or move a switch on the associate adapter tothe opposite position.

In a third embodiment, as an alternative for the LED indicators is touse a thermal indicator (as used in some batteries to indicate thecharging state). This may either be a “positive” indicator triggered bythe heat generated by the inductance or a “negative” indicator triggeredby the heat generated by a resistance placed in the non-inductivecircuit of the adapter. Such a solution is robust and inexpensive, butmay have a relatively slow response time (the discharge lamp has to burnfor several minutes to get an indication).

In yet another embodiment, equal inductances are placed in both circuitsof the extension means. This may consist of, for example, a coiled coil.Such a doubling will not increase losses but increases the size, weightand cost of the extension means. It will also have a strong negativeeffect on the preheating current during ignition.

A very favorable embodiment involves an automatic switching adapter.FIG. 4 shows an elongate extension means provided with an automaticswitching adapter 20 according to the invention. In addition, FIGS. 5Aand 5B shows two switching modes of the extension means 2 of FIG. 4. Inthe example of FIGS. 5A and 5B, the automatic switching adapter 20 isembodied in the form of a switch 31 which is loaded by a spring 33. Inthe switching mode of FIG. 5A, the switch 31 is cocked to a position inwhich the spring 33 is under tension. The switch 31 is held in thisposition by a small catch 32 attached to a bimetal strip 25. In theexample of FIG. 5A, a resistor 7 inserted in the non-inductive circuitof the extension means 2 is thermally coupled to this bimetal strip 25.If the extension means 2 is installed correctly, this resistor 7 willonly generate a small amount of heat during lamp ignition, which heatwill be insufficient for moving the bimetal strip 25 and releasing thecatch 32 on the switch 31. If the extension means 2 is installedincorrectly, the lamp current will flow through the resistor 7 coupledto the bimetal strip 25. After some minutes, the bimetal strip 25 willreach a sufficient temperature such that the deflection of the bimetalstrip 25 releases the catch 32 on the spring 33 loaded switch 31. Thiswill cause the switch 31 to move to the opposite position (see thearrows in FIGS. 5A and 5B), thus connecting the inductance 3 correctlyto the external ballast circuit 8 and placing the resistor 7 togetherwith the bimetal strip 25 in the external starter circuit 9. Switchingwill occur only once and only in 50% of installed adapters (others willremain in cocked position). When the low-pressure mercury vapordischarge lamp 1 is removed at the end of lamp life, the switch 31 inthe extension means 2 may be reset manually or automatically in theaction of assembling the extension means with a new lamp and insertingthem in the luminaire.

The benefits of the energy-saving low-pressure mercury vapor dischargelamp provided with extension means according to the invention include:approximately 15% lamp energy savings as compared with known TLD lampsand approximately 25% energy saving for known TL40 lamps. The lumenmaintenance is higher than 90% at 12,000 hours, whereas for “standard”color lamps the lumen maintenance is typically 70% at 8,000 hours. Inaddition, the lifetime is longer, the ignition behavior is improved, andthe extinction voltage is lower. In addition, the use of tri-phosphortechnology results in lower mercury consumption over life, meaning thatthe energy-saving low-pressure mercury vapor discharge lamps can have amercury dose less than half that of an equivalent “standard” color lamp,resulting in environmental benefits.

The measure according to the invention offers users of low-pressuremercury vapor discharge lamps with “standard colors” an incentive toswitch to low-pressure mercury vapor discharge lamps with tri-phosphortechnology.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.Use of the verb “comprise” and its conjugations does not exclude thepresence of elements or steps other than those stated in a claim. Thearticle “a” or “an” preceding an element does not exclude the presenceof a plurality of such elements. The invention may be implemented bymeans of hardware comprising several distinct elements, and by means ofa suitably programmed computer. In the device claim enumerating severalmeans, several of these means may be embodied by one and the same itemof hardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. An assembly of an elongate low-pressure mercury vapor discharge lamp(1) and at least one elongate extension means (2), the low-pressuremercury vapor discharge lamp comprising: a light-transmitting dischargevessel (10) enclosing, in a gastight manner, a discharge space (15)provided with a filling of mercury and a rare gas mixture, the rare gasmixture comprising at least 50% by volume of krypton, the dischargevessel (10) being provided with a luminescent layer (13), electrodes (4a; 4 b) being arranged in the discharge space (15) for maintaining adischarge in the discharge space (15), the elongate extension means (2)being provided for connection to the low-pressure mercury vapordischarge lamp (1), the extension means (2) comprising an inductance(3), the length of the low-pressure mercury vapor discharge lamp (1)together with the length of the extension means (2) being adapted to fita pre-determined mounting distance l_(md) of low-pressure mercury vapordischarge lamps.
 2. An assembly as claimed in claim 1, characterized inthat the impedance of the inductance (3) in the extension means (2) isin a range between 5% and 30% of the inductance of an external ballastcircuit (8) for the low-pressure mercury vapor discharge lamp.
 3. Anassembly as claimed in claim 1, characterized in that the gas pressurein the discharge vessel (10) of the low-pressure mercury vapor dischargelamp (1) is between 10⁵ and 4·10⁵ Pa, preferably between 2·10⁵ and 3·10⁵Pa.
 4. An assembly as claimed in claim 1, characterized in that theratio of the length l_(em) of the extension means (2) to the lengthl_(dl) of the low-pressure mercury vapor discharge lamp (1) is in arange of: ${0.8 \leq \frac{l_{dl}}{l_{dl} + l_{em}} \leq 0.98},$preferably in a range from 0.92 to 0.97.
 5. An assembly as claimed inclaim 1, characterized in that the rare gas mixture in the dischargevessel (10) of the low-pressure mercury vapor discharge lamp (1)comprises at least 80% by volume of krypton.
 6. An assembly as claimedin claim 1, characterized in that the extension means forms an integralpart of the low-pressure mercury vapor discharge lamp.
 7. An assembly asclaimed in claim 1, characterized in that the extension means (2)comprises two elongate extension parts (2 a, 2 b), the length of thelow-pressure mercury vapor discharge lamp (1) together with the lengthsof the two extension parts (2 a, 2 b) being adapted to fit thepre-determined mounting distance of low-pressure mercury vapor dischargelamps.
 8. An assembly as claimed in claim 1, characterized in that theextension means (2) is provided with an indicator means (18; 19) forindicating the status of the connection between the extension means (2)on the one hand and an external ballast circuit (8) and an externalstarter circuit (9) for the low-pressure mercury vapor discharge lamp(1) on the other hand.
 9. An assembly as claimed in claim 8,characterized in that the indicator means (18) comprises a lightemitting diode connected across turns of the inductance (3).
 10. Anassembly as claimed in claim 8, characterized in that the extensionmeans (2) comprises a resistor (7), and in that the indicator means (19)comprises a light emitting diode connected across the resistor (7). 11.An assembly as claimed in claim 8, characterized in that both circuitsof the extension means (2) comprise an inductance.
 12. An assembly asclaimed in claim 8, characterized in that the indicator means comprisesa thermal indicator.
 13. An assembly as claimed in claim 1,characterized in that the extension means (2) comprises an automaticswitching adapter (20) providing that, after the extension means (2)have been connected to the low-pressure mercury vapor discharge lamp (1)and the assembly has been plaeced in a standard external ballast circuit(8) and a standard external starter circuit (9), the inductance isautomatically connected to the external ballast circuit (8)independently of installation orientation.
 14. A low-pressure mercuryvapor discharge lamp (1) for use in an assembly as claimed in claim 1.15. An extension means (2) for use in an assembly as claimed in claim 1.